The present invention pertains to an optical pickup device wherein laser light is emitted toward an optical disk and said laser light is detected after being reflected from the optical disk.
Conventional optical pickup devices of this type include, for example, those similar to that shown at FIG. 6. In this optical pickup device, laser light is emitted from laser chip 101 and this laser light is split into a main beam and side beams at diffraction grating 102, the laser light, after being split in such fashion, exiting therefrom so as to be directed toward optical disk 106 by way of hologram 103, collimating lens 104, and objective lens 105. In addition, after being reflected at optical disk 106, said laser light is incident on hologram 103 by way of objective lens 105 and collimating lens 104; and this laser light being diffracted at hologram 103, only light of order 1 produced as a result of such diffraction is incident on photodiode 107. Accordingly, light of order 1 present in the main beam and light of order 1 present in the side beams is incident on photodiode 107. Photodiode 107 carries out photoelectric conversion with respect to light of order 1 present in the main beam to generate and output an RF signal, and carries out photoelectric conversion with respect to light of order 1 present in the side beams to generate and output a tracking error signal.
Furthermore, disclosed at Japanese Patent No. 2565185 is a device employing a nonpolarizing beamsplitter or a polarizing beamsplitter in place of the hologram 103 of the device at FIG. 6.
However, in the aforementioned conventional optical pickup devices, the efficiency with which laser light is utilized is low and there is, moreover, a high level of optical noise due to the laser light reflected from optical disk 106.
Laser light from the laser chip 101 is split at diffraction grating 102 and is diffracted at hologram 103, only light of order 0 therefrom reaching optical disk 106. In addition, laser light reflected from optical disk 106 is again diffracted by hologram 103, only light of order +1 therefrom being incident on photodiode 107. Here, taking the intensity of the laser light emitted from laser chip 101 to be 1, and taking the ratio of the intensities of the light of order 0 and of order ±1 produced as a result of diffraction by hologram 103 to be 1:4:1 (order −1:order order 0:order +1), because the fractional amount of light of order 0 reaching optical disk 106 by way of hologram 103 from laser chip 101 is 4/6, the fractional amount of light of order +1 incident on photodiode 107 by way of hologram 103 from optical disk 106 will be ( 4/6)×(⅙)=0.11, and it is clear that the efficiency with which laser light is utilized is low.
Furthermore, light of order 0 which is reflected from optical disk 106 and is transmitted through hologram 103 to return to laser chip 101 represents a source of optical noise. While attempts have been made to incline the stem of laser chip 101 or to paint the area around the optical path of the laser light black, this has not resulted in satisfactory reduction in optical noise.
Furthermore, in the device disclosed at Japanese Patent No. 2565185, because most of the light reflected from the optical disk returns to the laser chip by way of the nonpolarizing beamsplitter or the polarizing beamsplitter, the effect of optical noise has been large.
It is therefore an object of the present invention, which was conceived in light of the foregoing conventional problems, to provide an optical pickup device that utilizes laser light with high efficiency and that permits generation of optical noise to be held in check to a sufficient degree.